The present invention relates to an adapter for integrated circuit cards for cellular telephones.
In cellular telephone apparatus, in particular of the "GSM" type, the information relating to the subscriber and to the situation of the subscription of the cellular telephone are stored into a "smart card" known with the name of "SIM" (Subscriber Identification Module) provided with a microprocessor, which will be identified hereinafter as subscriber identification card.
This subscriber identification card allows, once inserted in a cellular telephone different from the one normally used by the subscriber, to perform telephone calls with a charge on the account of the subscriber owner of the same, independently from the GSM cellular telephone which is utilized.
The card may have two different formats. The first format is according to the ISO standards and has the dimensions of a conventional "credit card"; the second format is appreciably smaller, about as large as a stamp, and is known with the colloquial denomination "plug-in card".
For a normal utilizer of a GSM cellular telephone frequently the problem occurs of transferring his own subscriber identification card having one of the two formats above referred to, into a telephone apparatus that allows the introduction of subscriber identification cards having the other of the two formats.
While the conversion from the credit card format into the plug-in format cannot be performed, on the contrary the converse can be carried out, i.e. the conversion from the plug-in format into the credit card format.
A conversion of this kind is performed by inserting the plug-in card or element into a suitable adapter, which is a plastic card having the format of a credit card and having a housing for the plug-in card or element.
According to the prior art, adapter are known which comprise a single layer carrier having a rectangular opening on the front side for receiving the plug-in element; said rectangular opening being closed on the lower side by means of a film. Following the insertion of the plug-in element it is quite possible that this latter may slip out of the adapter following a possible bending or flexing of the same or a sudden shock of the same.
According to a second embodiment of the prior art, the adapter comprises a lower layer and an upper layer, both having on the front side to be inserted into the cellular telephone apparatus a rectangular opening for receiving the plug-in card; there results however an unevenness of the thickness of the adapter in the connection area with the cellular telephone apparatus, subjecting the adapter and the plug-in card to dangers of wearout or damaging following the connection and disconnection operations.
In a further embodiment according to the prior art, the adapter comprises a single layer having a door for receiving the plug-in element; the door having two button elements for its closure after the insertion of said element. Also in this case, unexpected openings, damages and wearout in the connection and disconnection operations may occur.
A common disadvantage of such embodiments according to the prior art consists in the fact that there is provided an insertion area of the plug-in element in correspondence with the connection area of the adapter with the cellular telephone.
EP-A-0 564 105 discloses a memory module adapter comprising a circuit board having contacts, the size and configuration of which is compatible with a reader for a first memory module such as a credit card sized Subscriber Identity Module card. This adapter however has the inconvenience that the connector for the plug-in module has a thickness much greater than the thickness of the credit card, being therefore impossible its insertion into a telephone set that has a narrow slit, substantially corresponding in width to the actual thickness of the credit card sized Subscriber Identity Module card.